In our prior Australian Pat. No. 488,652, a novel approach to the production of security tokens--particularly bank-notes--was disclosed and the serious problems which confront conventional bank notes with respect to forgery were described. The security token or bank-note disclosed in Patent No. 488,652 comprised a substrate of opaque thermoplastic sheet material intimately bonded to a web of woven or unwoven thermoplastic fibres, the substrate being printed as desired and having bonded thereon one or more optically-variable security devices. The fibrous web was employed to impart durability, crumple-resistance and tear-strength to the note. Where a security device (such as a Moire pattern) was employed which depended for its optically variable properties upon the transmission of light, it was necessary to punch out a hole in the substrate, insert the device and bond it in place with further layers of (transparent) plastic sheet material.
Although samples of bank-notes formed in this way performed most satisfactorily with respect to conventional notes regarding durability and security, they were complex and relatively expensive. Moreover, when transmission security devices were inserted in pockets in the substrate, an area of weakness and high stress was created which reduced both durability and security.